Hi. We are traveling to Milan early April and are booked for 10 days in Bellagio on Lake Como. (We wanted to stay in Varenna, but hotel is booked). We are young seniors who love to walk, see nature, learn about local culture and are foodies. My initial thought was to do some day trips to Bologna and Verona. However, after looking at train travel times, that doesn’t seem wise. I am concerned that 10 days on Como may be too long. My question is, should we leave as is and not explore Bologna/Verona or perhaps spend half the time on Como and the other half in Florence and do day trips to Bologna/Verona from there? (We have previously been to Venice, Florence, Tuscany and Rome.) We will spend our last day in Milan as we fly home from there.
Your thoughts and recommendations are much appreciated!

I’d break it as half (or less) in Como and the rest in Bologna. Lots of easy day trips from Bologna, including Verona.

If you liked the original idea of lake time with walking, nature, etc., another option for splitting the nights is Lugano. It's an easy bus ride from Menaggio (after the ferry from Bellagio) or a short train ride from Como (again, after the ferry from Bellagio). The train from Lugano to Milano Centrale takes a little over an hour, no change. Bellinzona is a nice day trip from Lugano... about 15 minutes by train. Funiculars to Monte San Salvatore and Monte Bre are just outside Lugano.

FWIW, my choice would be to spend more than one day in Milan.

Jean is right. There is much more to see and to do in and around Lugano. The network of well signmarked panoramic hiking trails in the Lugano area is much better.
In the Lugano area you can furthermore use 6 different cog wheel railways, rope railways and gondolas to view points over lakes and up to the Alps (Mont Blanc, Matterhorn, Piz Bernina, Ortles, etc).
Many bus lines into unspoilt mountaiin valleys like Val di Muggio, Valle Mara, Val Colla, Val d'Isone......
the Unesco World heritage sites around Lugano can easily be reached by frequent trains
Most Lugano hotel keepers will give you a Passs for free ride on local train and bus lines.
Direct trains from Lugano to Malpensa airport MXP every hr.
Direct trains to Milano Centrale at least every hr.
Direct trains to Lake Lucerne (1 hr journey) every hr
Direct trains from Lugano to
Parma - Modena - Bologna,
Brescia - Peschiera del Garda - Verona - Venice
Pavia - Genova